Why did the Romans want to stop the spread of Christianity?

The Romans were ever alert to revolution within their empire. A usual sign of a plot was when people started taking secret oaths and binding themselves with activity which would incur the death penalty to stop participants turning state evidence.

The sight of Christians having meetings in private houses instead of going up to the temple like honest folk, and taking oaths drinking blood and eating human flest alarmed the Romans that this presaged a political plot. They reacted accordingly. A couple of letters from Plimy the Younger, governor of Bythinia, to empror Trajan are very illustrative of this.